The primary goals for the Biosensor Initiative are to continue to develop biosensors for key regulatory and effector nodes in cell migration and to use existing and proposed biosensors to acquire quantitative data that can be used to develop an experimentally verified theoretical model of cell migration by the Modeling Initiative and others in the modeling community. The Initiative builds on the sensor technologies, fluorescence assays, high throughput microscopy and collaborations from the first CMC funding period to move into Phase II, wherein we plan to visualize signaling events in living cells and to acquire and analyze large microscopic data sets. The modeling will be carried out as a close collaboration with the Modeling Initiative. A major focus of the Initiative will be Rho family regulators since they control key migration nodes. In addition the Initiative will focus on construction of biosensors and photoactivatable reagents, using both existing and new technologies, for key upstream and downstream members of these signaling pathways. In the end we produce a detailed experimental and mathematical analysis of a specific, critical signaling pathway in cell migration.